Improved ethylene polymerization catalyst composition

Abstract

Ziegler-Natta catalyst composition capable of producing ethylene / alpha-olefins copolymers, particularly linear low density polyethylene; the composition having an improved stability of its behaviour during polymerization in respect to time. The Ziegler-Natta catalyst composition comprises: 1. Ziegler-Natta catalyst composition for the production of ethylene copolymers comprising A) a procatalyst, which procatalyst comprises a) an Al compound having the formula Al(alkyl)xCl3-x (I), where alkyl is an alkyl group with 1 to 12 and 0 = x = 3, b) a magnesium hydrocarbyloxy compound of formula Mg(OR1)2-n(R2)n (II), wherein each R1 and R2 is independently a C1-20 hydrocarbon residue which may optionally be substituted with halogen and 0 = n yTi(OR3)4-y (III), wherein R3 is a C2-20 hydrocarbon residue and y is 1, 2, 3 or 4, with compounds a), b) and c); being supported on a particulate inorganic carrier and B) a halogenated aluminium alkyl cocatalyst of the formula (IV) (C1-C4-alkyl)m-Al-X3-m, wherein X is chlorine, bromine, iodine or fluorine and m is 1 or 2.

Description

technical field [0001] The present invention relates to Ziegler-Natta catalyst compositions suitable for the preparation of ethylene polymers, especially linear low density polyethylene. [0002] More particularly, the present invention relates to Ziegler-Natta catalyst compositions capable of producing ethylene / α-olefin copolymers, especially linear low density polyethylene, and which have a time-dependent Improved performance stability. The composition comprises a mixture comprising a Group 13 metal, chlorine, magnesium and titanium atoms supported on a particulate inorganic support and an alkylaluminum halide as a cocatalyst. Background technique [0003] Typically, ethylene, alone or together with other ethylenically unsaturated monomers, is polymerized in the presence of a catalyst composition having two essential components: a transition metal compound of any group (commonly referred to as procatalyst); and a metal compound belonging to Group 1, 2 or 13 of said perio...

AI Technical Summary

Problems solved by technology

[0020] For example, this catalyst composition shows a change in comonomer response over time, resulting in a significant decrease in comonomer incorporation during the first phase of polymerization.

This further leads to an increase in density during the copolymerization

[0021] A further disadvantage is that the use of usual Ziegler-Natta catalyst compositions often leads to a significant decrease in the melt flow rate (MRF) and a respective increase in the molecular weight during the first phase of the copolymerization

[0022] If the polymerization process is a continuous multistage process, this so-called "time drift" in catalyst performance can cause further problems, where the residence time distribution combined with the "time drift" problem can lead to inhomogeneity of the polymer produced

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